Lithographic apparatus and a method of operating the apparatus

ABSTRACT

A lithographic apparatus is disclosed that includes a projection system, and a liquid confinement structure configured to at least partly confine immersion liquid to an immersion space defined by the projection system, the liquid confinement structure and a substrate and/or substrate table. Measures are taken in the lithographic apparatus, for example, to reduce the effect of droplets on the final element of the projection system or to substantially avoid such droplet formation.

This application claims priority and benefit under 35 U.S.C. §119(e) toU.S. Provisional Patent Application No. 61/097,743, entitled“Lithographic Apparatus and a Method of Operating the Apparatus”, filedon Sep. 17, 2008, to U.S. Provisional Patent Application No. 61/150,106,entitled “Lithographic Apparatus and a Method of Operating theApparatus”, filed on Feb. 5, 2009, and to U.S. Provisional PatentApplication No. 61/174,826, entitled “Lithographic Apparatus and aMethod of Operating the Apparatus”, filed on May 1, 2009. The content ofeach of the foregoing applications is incorporated herein in itsentirety by reference.

FIELD

The present invention relates to an immersion lithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe present invention will be described with reference to liquid.However, another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

Submersing the substrate or substrate and substrate table in a bath ofliquid (see, for example, U.S. Pat. No. 4,509,852) means that there is alarge body of liquid that should be accelerated during a scanningexposure. This may require additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

In an immersion apparatus, immersion fluid is handled by a fluidhandling system, structure or apparatus. In an embodiment the fluidhandling system may supply immersion fluid and therefore be a fluidsupply system. In an embodiment the fluid handling system may at leastpartly confine immersion fluid and thereby be a fluid confinementsystem. In an embodiment the fluid handling system may provide a barrierto immersion fluid and thereby be a barrier member, such as a fluidconfinement structure. In an embodiment the fluid handling system maycreate or use a flow of gas, for example to help in controlling the flowand/or the position of the immersion fluid. The flow of gas may form aseal to confine the immersion fluid so the fluid handling structure maybe referred to as a seal member; such a seal member may be a fluidconfinement structure. In an embodiment, immersion liquid is used as theimmersion fluid. In that case the fluid handling system may be a liquidhandling system. In reference to the aforementioned description,reference in this paragraph to a feature defined with respect to fluidmay be understood to include a feature defined with respect to liquid.

One of the arrangements proposed is for a liquid supply system toprovide liquid on only a localized area of the substrate and in betweenthe final element of the projection system and the substrate using aliquid confinement system (the substrate generally has a larger surfacearea than the final element of the projection system). One way which hasbeen proposed to arrange for this is disclosed in PCT patent applicationpublication no. WO 99/49504. As illustrated in FIGS. 2 and 3, liquid issupplied by at least one inlet IN onto the substrate, preferably alongthe direction of movement of the substrate relative to the finalelement. Liquid is removed by at least one outlet OUT after havingpassed under the projection system. That is, as the substrate is scannedbeneath the element in a −X direction, liquid is supplied at the +X sideof the element and taken up at the −X side. FIG. 2 shows the arrangementschematically in which liquid is supplied via inlet IN and is taken upon the other side of the element by outlet OUT which is connected to alow pressure source. In the illustration of FIG. 2 the liquid issupplied along the direction of movement of the substrate relative tothe final element, though this does not need to be the case. Variousorientations and numbers of in- and out-lets positioned around the finalelement are possible, one example is illustrated in FIG. 3 in which foursets of an inlet with an outlet on either side are provided in a regularpattern around the final element.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PS andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PS, causing a flow of a thin film of liquid betweenthe projection system PS and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another arrangement which has been proposed is to provide the liquidsupply system with a liquid confinement member which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5. The liquid confinement member is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). A seal is formed between the liquid confinementand the surface of the substrate. In an embodiment, a seal is formedbetween the liquid confinement structure and the surface of thesubstrate and may be a contactless seal such as a gas seal. Such asystem is disclosed in United States patent application publication no.US 2004-0207824, hereby incorporated in its entirety by reference.

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, each herebyincorporated in their entirety by reference, the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

After exposure of a substrate in an immersion lithographic apparatus,the substrate table is moved away from its exposure position to aposition in which the substrate may be removed and replaced by adifferent substrate. This is known as substrate swap. In a two stagelithographic apparatus, for example ASML's “Twinscan” lithographicapparatus, the substrate tables swap takes place under the projectionsystem.

PCT patent application publication WO 2005/064405 discloses an all wetarrangement in which the immersion liquid is unconfined. In such asystem the whole top surface of the substrate is covered in liquid. Thismay be advantageous because then the whole top surface of the substrateis exposed to the substantially same conditions. This may have anadvantage for temperature control and processing of the substrate. In WO2005/064405, a liquid supply system provides liquid to the gap betweenthe final element of the projection system and the substrate. Thatliquid is allowed to leak over the remainder of the substrate. A barrierat the edge of a substrate table prevents the liquid from escaping sothat it can be removed from the top surface of the substrate table in acontrolled way. Although such a system improves temperature control andprocessing of the substrate, evaporation of the immersion liquid maystill occur. One way of helping to alleviate that problem is describedin United States patent application publication no. US 2006/0119809. Amember is provided which covers the substrate W in all positions andwhich is arranged to have immersion liquid extending between it and thetop surface of the substrate and/or substrate table which holds thesubstrate.

The immersion system may be a fluid handling system or apparatus. In oneembodiment the fluid handling system may supply immersion fluid orliquid and therefore be a fluid or liquid supply system. In anembodiment the fluid handling system may confine fluid or liquid andthereby be a fluid or liquid confinement system. In an embodiment thefluid handling system may provide a barrier to fluid or liquid andthereby be a barrier member. In an embodiment the fluid handling systemmay create or use a flow of gas, for example to help in handling liquid.In an embodiment immersion liquid rather than immersion fluid is used.In that case the fluid handling system may be a liquid handling system.The fluid handling system is located between the projection system andthe substrate table.

In a fluid handling system or liquid confinement structure, liquid isconfined to a space, for example within a confinement structure by thebody of the structure, the underlying surface (e.g. a substrate table, asubstrate supported on the substrate table, a shutter member and/or ameasurement table) and, in the case of a localized area immersionsystem, a liquid meniscus between the fluid handling system or liquidconfinement structure and the underlying structure i.e. in an immersionspace. In the case of an all wet system, liquid is allowed to flow outof the immersion space onto the top surface of the substrate and/orsubstrate table.

SUMMARY

Droplets of liquid may splash onto the part of the final element of theprojection system which is not normally in contact with immersion liquidin the immersion space. Such droplets can then evaporate forming coldspots on the last optical (e.g., lens) element leading to imaging errorsand/or focusing errors.

Also, evaporation of liquid around the line defining the boundarybetween the liquid in the immersion space, gas and the final element ofthe projection system can have a strong effect on thermal disturbanceson the final element of the projection system. This contact line canmove due to sloshing of immersion liquid during relative motion betweenthe liquid confinement structure and the substrate. When the line movesdown a thin film of liquid can be left behind which evaporates andthermally disturbs the final element of the projection system.

It is therefore desirable, for example, to provide a system to reducethe effect of droplets and/or the gas-liquid final element interface onthe final element or substantially to avoid such droplet formation.

In an aspect, there is provided a lithographic apparatus, comprising aprojection system; a liquid confinement structure configured at leastpartly to confine immersion liquid to an immersion space defined by theprojection system, the liquid confinement structure and a substrateand/or substrate table; and a barrier extending from the projectionsystem to the liquid confinement structure and around the optical axisof the apparatus to substantially seal a gap between the projectionsystem and the liquid confinement structure, wherein the barrier iscompliant substantially to prevent transmission of forces between theprojection system and the liquid confinement structure.

In an aspect, there is provided a lithographic apparatus, comprising: aprojection system; a liquid confinement structure to at least partlyconfine immersion liquid to an immersion space defined by the projectionsystem, the liquid confinement structure and a substrate and/orsubstrate table; and a device to force immersion liquid in a radiallyoutward direction and in contact with a surface of the final element ofthe projection system and/or to maintain liquid in contact with thesurface of the final element of the projection system radially outwardof a meniscus extending, in use, between the projection system and theliquid confinement structure.

In an aspect, there is provided a lithographic apparatus wherein anoptical element insulator is located between an optically active part ofa projection system and a liquid confinement structure and the opticalelement insulator lies outside of an optical path of the apparatus.

In an aspect, there is provided A lithographic apparatus, comprising aprojection system; and a liquid confinement structure configured atleast partly to confine immersion liquid to an immersion space definedby projection system, the liquid confinement structure and a substrateand/or substrate table, wherein the liquid confinement structure ispartitioned into an upper volume and a lower volume which are separatedby a transmissive plate, wherein the liquids in the upper volume and thelower volume are different.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a fluid handling structure as a liquid supplysystem for use in a lithographic projection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, a liquid confinement structure whichmay be used in an embodiment of the present invention as a liquid supplysystem;

FIG. 6 depicts, in cross-section, a liquid confinement structure andprojection system according to an embodiment of the invention;

FIG. 7 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 8 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 9 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 10 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 11 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 12 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 13 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 14 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 15 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 16 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention;

FIG. 17 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention; and

FIG. 18 depicts, in cross-section, a liquid confinement structure andprojection system in accordance with a further embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation or DUV radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT holds the patterning device. The supportstructure MT holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structureMT can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure MT maybe a frame or a table, for example, which may be fixed or movable asdesired. The support structure MT may ensure that the patterning deviceis at a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system. The types of projectionsystem may include: refractive, reflective, catadioptric, magnetic,electromagnetic and electrostatic optical systems, or any combinationthereof. The selection or combination of the projection system is asappropriate for the exposure radiation being used, or for other factorssuch as the use of an immersion liquid or the use of a vacuum. Any useof the term “projection lens” herein may be considered as synonymouswith the more general term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more patterning device tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as n-outer andn-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS.The projection system focuses the beam onto a target portion C of thesubstrate W. With the aid of the second positioner PW and positionsensor IF (e.g. an interferometric device, linear encoder or capacitivesensor), the substrate table WT can be moved accurately, e.g. so as toposition different target portions C in the path of the radiation beamB. Similarly, the first positioner PM and another position sensor (whichis not explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

In another mode, the support structure MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as desired after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

An arrangement to provide liquid between a final element of theprojection system PS and the substrate is the so called localizedimmersion system IH. In this system a liquid handling system is used inwhich liquid is only provided to a localized area of the substrate. Thespace filled by liquid is smaller in plan than the top surface of thesubstrate and the area filled with liquid remains substantiallystationary relative to the projection system PS while the substrate Wmoves underneath that area. Four different types of localized liquidsupply systems are illustrated in FIGS. 2-5. The liquid supply systemsdisclosed in FIGS. 2-4 were described above.

FIG. 5 schematically depicts a localized liquid supply system with aliquid confinement structure 12. The liquid confinement structureextends along at least a part of a boundary of the space between thefinal element of the projection system and the substrate table WT orsubstrate W. (Please note that reference in the following text tosurface of the substrate W also refers in addition or in the alternativeto a surface of the substrate table, unless expressly stated otherwise.)The liquid confinement structure 12 is substantially stationary relativeto the projection system in the XY plane though there may be somerelative movement in the Z direction (in the direction of the opticalaxis). In an embodiment, a seal is formed between the liquid confinementstructure and the surface of the substrate W and may be a contactlessseal such as fluid seal, desirably a gas seal.

The liquid confinement structure 12 at least partly contains liquid inthe immersion space 11 between a final element of the projection systemPS and the substrate W. A contactless seal 16 to the substrate W may beformed around the image field of the projection system so that liquid isconfined within the space between the substrate W surface and the finalelement of the projection system PS. The immersion space is at leastpartly formed by the liquid confinement structure 12 positioned belowand surrounding the final element of the projection system PS. Liquid isbrought into the space below the projection system and within the liquidconfinement structure 12 by liquid inlet 13. The liquid may be removedby liquid outlet 13. The liquid confinement structure 12 may extend alittle above the final element of the projection system. The liquidlevel rises above the final element so that a buffer of liquid isprovided. In an embodiment, the liquid confinement structure 12 has aninner periphery that at the upper end closely conforms to the shape ofthe projection system or the final element thereof and may, e.g., beround. At the bottom, the inner periphery closely conforms to the shapeof the image field, e.g., rectangular, though this need not be the case.

In an embodiment, the liquid is contained in the immersion space 11 by agas seal 16 which, during use, is formed between the bottom of theliquid confinement structure 12 and the surface of the substrate W.Other types of seal are possible, as is no seal (for example in an allwet embodiment) or a seal achieved by capillary forces between theundersurface of the liquid confinement structure 12 and a facingsurface, such as the surface of a substrate W, a substrate table WT or acombination of both.

The gas seal 16 is formed by gas, e.g. air or synthetic air but, in anembodiment, N₂ or another inert gas. The gas in the gas seal 16 isprovided under pressure via inlet 15 to the gap between liquidconfinement structure 12 and substrate W. The gas is extracted viaoutlet 14. The overpressure on the gas inlet 15, vacuum level on theoutlet 14 and geometry of the gap are arranged so that there is ahigh-velocity gas flow 16 inwardly that confines the liquid. The forceof the gas on the liquid between the liquid confinement structure 12 andthe substrate W contains the liquid in an immersion space 11. Theinlets/outlets may be annular grooves which surround the space 11. Theannular grooves may be continuous or discontinuous. The flow of gas iseffective to contain the liquid in the space 11. Such a system isdisclosed in United States patent application publication no. US2004-0207824.

Other arrangements are possible and, as will be clear from thedescription below, an embodiment of the present invention may use anytype of localized liquid supply system as the liquid supply system.

One or more localized liquid supply systems seal between a part of theliquid supply system and a substrate W. The seal may be defined by ameniscus of liquid between the part of the liquid supply system and thesubstrate W. Relative movement of that part of the liquid supply systemand the substrate W may lead to breakdown of the seal, for example themeniscus, and thereby leaking of liquid. The problem may be moresignificant at high scan velocities. An increased scan velocity isdesirable because throughput increases.

FIG. 6 illustrates a liquid confinement structure 12 which is part of aliquid supply system. The liquid confinement structure 12 extends aroundthe periphery (e.g., circumference) of the final element of theprojection system PS in a plane parallel to the top surface of thesubstrate table and/or perpendicular to the optical axis such that theliquid confinement structure (which is sometimes called a barrier memberor seal member) is, for example, substantially annular in overall shape.That is, the liquid confinement structure encloses the last optical(e.g., lens) element. The liquid confinement structure 12 may be anannulus and may be ring-shaped. The projection system PS may not becircular and the outer edge of the liquid confinement structure 12 mayalso not be circular so that it is not necessary for the liquidconfinement structure 12 to be ring shaped. The liquid confinementstructure could also be other shapes so long as it has an openingthrough which the projection beam may pass out from the final element ofthe projection system PS. The opening may be centrally located. Thus,during exposure, the projection beam may pass through liquid containedin the opening of the liquid confinement structure and onto thesubstrate W. The liquid confinement structure 12 may be, for example,substantially rectangular and may not be necessarily the same shape asthe final element of the projection system PS is at the height of theliquid confinement structure 12.

The function of the liquid confinement structure 12 is at least partlyto maintain or confine liquid in the space 11 between the projectionsystem PS and the substrate W so that the projection beam may passthrough the liquid. That space 11 is known as the immersion space. Thetop level of liquid is simply contained by the presence of the liquidconfinement structure 12. The level of liquid in the space is maintainedsuch that the liquid does not overflow over the top of the liquidconfinement structure 12.

The immersion liquid is provided to the space 11 by the liquidconfinement structure 12 (thus the liquid confinement structure 12 maybe considered to be a fluid handling structure). A passageway or flowpath for immersion liquid passes through the liquid confinementstructure 12. Part of the flow path is comprised by a chamber 26. Thechamber 26 has two side walls 28, 22. Liquid passes from chamber 24through the first side wall 28 into chamber 26 and then through thesecond side wall 22 into the space 11. A plurality of outlets 20 providethe liquid to the space 11. The liquid passes through through-holes 29,20 in side walls 28, 22 respectively prior to entering the space 11. Thelocation of the through holes 20, 29 may be irregular.

A seal is provided between the bottom of the liquid confinementstructure 12 and the substrate W (This feature indicates that the liquidconfinement structure 12 may be a fluid handling structure). In FIG. 6 aseal device is configured to provide a contactless seal and is made upof several components. Radially outwardly from the optical axis of theprojection system PS, there is provided a (optional) flow control plate50 which extends into the space (though not into the path of theprojection beam) which helps maintain substantially parallel flow of theimmersion liquid out of outlet 20 across the space. The flow controlplate 50 has through holes 55 in it to reduce the resistance to movementin the direction of the optical axis of the liquid confinement structure12 relative to the projection system PS and/or substrate W.

Radially outwardly of the flow control plate 50 on the bottom surface ofthe liquid confinement structure 12 may be an inlet 180. The inlet 180can provide liquid in a direction towards the substrate W. Duringimaging this may be useful in preventing bubble formation in theimmersion liquid by filling a gap between the substrate W and substratetable WT with liquid.

Radially outwardly of the inlet 180 may be an extractor assembly 70 toextract liquid from between the liquid confinement structure 12 and thesubstrate W and/or the substrate table WT. The extractor assembly 70will be described in more detail below and forms part of the contactlessseal which is created between the liquid confinement structure 12 andthe substrate W. The extractor assembly 70 may operate as a single phaseor as a dual phase extractor.

Radially outwardly of the extractor assembly 70 may be a recess 80. Therecess is connected through an inlet 82 to the atmosphere. The recess 80is connected via an outlet 84 to a low pressure source. The inlet 82 mayradially outwardly positioned with respect to the outlet 84. Radiallyoutwardly of the recess 80 may be a gas knife 90. An arrangement of theextractor assembly, recess and gas knife is disclosed in detail inUnited States patent application publication no. US 2006/0158627,incorporated herein its entirety by reference. However, in that documentthe arrangement of the extractor assembly is different.

The extractor assembly 70 comprises a liquid removal device or extractoror inlet such as the one disclosed in United States patent applicationpublication no. US 2006-0038968, incorporated herein its entirety byreference. Any type of liquid extractor may be used. In an embodiment,the liquid removal device 70 comprises an inlet which is covered in aporous material 110 which is used to separate liquid from gas to enablesingle-liquid phase liquid extraction. A chamber 120 downstream of theporous material 110 is maintained at a slight under pressure and isfilled with liquid. The under pressure in the chamber 120 is such thatthe meniscuses formed in the holes of the porous material 110 preventambient gas from being drawn into the chamber 120 of the liquid removaldevice 70. However, when the surface of the porous material 110 comesinto contact with liquid there is no meniscus to restrict flow and theliquid can flow freely into the chamber 120 of the liquid removal device70. The surface of the porous material 110 extends radially inwardlyalong the liquid confinement structure 12 (as well as around the space).The rate of extraction through the surface of the porous material 110varies according to how much of the porous material 110 is covered byliquid.

The porous material 110 has a large number of small holes each with adimension, e.g. a width, such as a diameter, d_(hole) in the range of 5to 50 μm. The porous material 110 may be maintained at a height in therange of 50 to 300 μm above a surface from which liquid is to beremoved, e.g. the surface of a substrate W. In an embodiment, porousmaterial 110 is at least slightly liquidphilic, i.e. having a contactangle of less than 90°, desirably less than 85° or desirably less than80°, to the immersion liquid, e.g. water.

It may not always be possible to prevent gas being drawn into the liquidremoval device but the porous material 110 will prevent large unevenflows that may cause vibration. Micro-sieves made by electroforming,photoetching and/or laser cutting can be used as the porous material110. Suitable sieves are made by Stork Veco B.V., of Eerbeek, theNetherlands. Other porous plates or solid blocks of porous material mayalso be used, provided the pore size is suitable to maintain a meniscuswith the pressure differential that will be experienced in use.

During scanning of the substrate W (during which the substrate W movesunder the liquid confinement structure 12 and projection system PS) themeniscus 115 extending between the substrate W and the liquidconfinement structure 12 may be drawn either towards or away from theoptical axis by a drag force applied by the moving substrate W. This canlead to liquid loss which may result in: evaporation of the liquid,cooling of the substrate W, and consequent shrinkage and overlay errorsas described above. Liquid stains may also or alternatively be leftbehind from interaction between the liquid droplets and resistphotochemistry.

Although not specifically illustrated in FIG. 6, the liquid supplysystem has an arrangement to deal with variations in the level of theliquid. This is so that liquid which builds up between the projectionsystem PS and the liquid confinement structure 12 can be dealt with anddoes not spill. Such a build-up of liquid might occur during relativemovement between the liquid confinement structure 12 and the projectionsystem PS described below; such movement may be referred to as sloshing.One way of dealing with this liquid is to provide the liquid confinementstructure 12 so that it is very large so that there is hardly anypressure gradient over the periphery (e.g., circumference) of the liquidconfinement structure 12 during relative movement between the liquidconfinement structure 12 and the projection system PS. In an alternativeor additional arrangement, liquid may be removed from the top of theliquid confinement structure 12 using, for example, an extractor such asa single phase extractor similar to the extractor assembly 70. Analternative or additional feature is a liquidphobic (e.g., hydrophobic)coating. The coating may form a band around the top of the liquidconfinement structure 12 surrounding the opening and/or around the last(optical) element of the projection system PS. The coating may beradially outward of the optical axis of the projection system PS. Theliquidphobic (e.g., hydrophobic) coating helps keep the immersion liquidin the space 11.

An embodiment of the present invention will be described with referenceto a liquid confinement structure 12 with the above mentioned structure.However, it will be apparent that any other type of liquid confinementstructure or liquid handling system which provides liquid to animmersion space between the final element of the projection system PSand a substrate W may be applied in an embodiment of the invention. Aliquid confinement structure or fluid handling system of both alocalized area immersion lithographic apparatus and an all wetarrangement may be applied in an embodiment of the invention.

An embodiment of the invention is intended to help solve the problem ofcold spots forming on the last optical element caused by evaporatingdroplets. An embodiment of the invention may prevent evaporation of adroplet 205 within a gas space 200, which could apply an unwanted heatload to a) the liquid confinement structure 12 (although this is not assignificant a problem as for the last element); and/or b) the lastoptical element. A solution is to have an environment saturated or nearsaturated with vapor of the immersion liquid in a gas space 200 betweenthe final element of the projection system PS, the liquid confinementstructure 12 and the immersion space 11. Hereinafter saturated gas willbe referred to. This term is intended to include near saturated gas orgas with a vapor pressure of immersion liquid at a level of at least 50%or 60% or 75% or 80% or 90% of the vapor pressure at saturation. The gasis retained by a barrier 220. Different forms of barrier 220 areillustrated in FIGS. 6-9.

The barrier 220 is desirably positioned relative to the optical axis tooptimize, e.g. maximize, the benefit of the volume of the gas space 200.The gas space 220 may define an environment of a gas saturated or almostsaturated with immersion liquid vapor. The gas space 220 may bedesirable for the reasons provided in the previous paragraph. The gaswithin the gas space 200 is confined relative to the gas radiallyoutward of the barrier 220. That is, the gas outside the barrier 220 maybe entrained in a gas flow. Therefore it may be advantageous to positionthe barrier 220 as far radially outwardly as possible. This wouldminimize the radially outward portion of the volume between the liquidconfinement structure 12 and the final element of the projection system.However, this needs to be balanced against possible loss in through-putif the gas space 200 is too large; it takes time to achieve equilibriumin the gas space 200 and the larger it is the longer it takes to achieveequilibrium which should be achieved before scanning starts. As with allembodiments, it may be desirable to ensure that at least all of thesurface, e.g. the downwardly facing surface, of the final element of theprojection system is protected from high thermal loads. Therefore, asshown in FIG. 6, the barrier 220 is provided at the radially outwardedge 235 of the final element of the projection system. Alternativelythe barrier 220 may be provided further radially outwardly. In anembodiment the barrier 220 is provided radially inwardly of the outwardedge 235 (see FIG. 8).

Below a certain threshold of saturation in gas, immersion liquidevaporates. Evaporation of liquid, for example as a droplet or a film(hereinafter droplet includes reference to film unless otherwisestated), applies a heat load to the surface on which it is located. Ator above the certain threshold of saturation evaporation issignificantly reduced, if not stopped. The gas is saturated with theimmersion liquid vapor. Thus the evaporation can be reduced orsuppressed by ensuring that the entire area that can reduce opticalperformance if a cold spot is formed on it by evaporation, is surroundedby saturated gas (saturated enough to avoid evaporation of fluid). Thisvolume can be enclosed by using a barrier 220 between the liquidconfinement structure 12 and the final element of the projection systemPS. If evaporation is avoided, the temperature offset is avoided andtherefore the optical aberration is avoided.

Because the saturated gas prevents evaporation of droplets on, forexample, the projection system PS, the saturated gas can be consideredan insulator. That is, the presence of saturated gas avoids anevaporational heat load being applied to an applicable surface such asthe projection system PS. The saturated gas therefore has an insulatingeffect on the applicable surface such as the projection system PS (andin particular on the final element of the projection system PS (which isin contact with immersion liquid)). Therefore, the saturated gas is aninsulator or isolator present between the projection system PS and theliquid confinement system.

In FIG. 6 a gas space 200 is positioned underneath the projection systemPS and above the liquid confinement structure 12. Saturated gas can becontained or confined in the gas space 200. Radially inwardly the gasspace is bounded by a meniscus 210 of liquid of the immersion space 11.Radially outwardly the humid gas space 200 is bounded by a barrier 220.

In the FIG. 6 embodiment the barrier 220 is in the form of a bellows.The barrier 220 extends from the projection system PS to the liquidconfinement structure 12. The barrier extends around the optical axis ofthe apparatus thereby to seal a gap between the projection system PS andthe liquid confinement structure 12 to define the gas space 200. Becausethe barrier 220 is in the form of a bellows, the barrier 220 iscompliant substantially to prevent transmission of forces between theprojection system PS and the liquid confinement structure 12.

Although the barrier 220 is illustrated as being connected between andattached to the final element of the projection system PS and the liquidconfinement structure 12, this is not necessarily the case. For example,the barrier 220 could extend from a mounting or shielding structure ofthe projection system PS to the liquid confinement structure 12.

The barrier 220 is attached at one end to the projection system PS andat the other end to the liquid confinement structure 12. However, thatis not necessarily the case. In one embodiment, the barrier 220 is notattached at one or both ends and is in contact with the projectionsystem PS and/or the liquid confinement structure 12. The barrier 220may be held in contact with at least one of the projection system PS andliquid confinement structure 12 by the elasticity of the material of thebarrier 220.

The barrier 220 seals the gap between the projection system PS and theliquid confinement structure 12. Thereby the barrier 220 partly definesthe gas space 200. The gas space 200 is defined by the barrier 220, theprojection system PS, the meniscus 210 extending between the projectionsystem PS and the liquid confinement structure 12.

Desirably the barrier 220 has a stiffness in the direction of theoptical axis of less than 1 N/mm, desirably less than 0.5 N/mm.

In one embodiment a saturated gas source 250 may be provided whichsupplies gas through an orifice 255 in the liquid confinement structure12 to the gas space 200. Thereby saturated gas can be replenished to thegas space 200. There may be an opening, for example in the liquidconfinement structure 12, to extract gas from the gas space 200. Theopening may also serve to remove liquid from the immersion space 11. Anadvantage of this is that because any gas present would be saturated,this would prevent evaporation in the fluid removal system. Also theextracted gas could be resupplied by the saturated gas source 250 to thegas space 200. Alternatively the opening could be solely for gasextraction and one or more separate openings could be provided forremoval of liquid from the immersion space 11.

As can be seen, the barrier 220 partitions the space between theprojection system PS and the liquid confinement structure 12 into aradially inward space for the saturated gas (i.e. the gas space 200) anda radially outward part in fluid communication with the externalatmosphere radially outwardly of the liquid confinement structure 12 andprojection system PS.

FIG. 7 illustrates a further embodiment which is the same as theembodiment of FIG. 6 except as described below.

In the embodiment illustrated in FIG. 7 the barrier 220 is in the formof a seal, for example an elongate seal, which is attached to theprojection system PS and is in contact with the liquid confinementstructure 12 due to the elasticity of the material of the barrier 220.Alternatively the barrier 220 may be attached to the liquid confinementstructure 12 and in contact with the projection system PS due to theelasticity of the material of the barrier 220. The barrier 220 is, incross-section, substantially L shaped. A surface rather than an end ofthe barrier 220 contacts the projection system PS or liquid confinementstructure 12 at its free end. The barrier 220 may be made of polymer,such as a fluoropolymer (e.g. viton).

FIG. 8 illustrates a further embodiment which is the same as theembodiment of FIG. 7 except as described below.

In the FIG. 8 embodiment the barrier 220 is, in cross-section, agenerally V-shaped. The barrier 220 is similar to a leaf spring. It maybe glued, adhered or attached along one side of the V to the projectionsystem PS. The barrier 220 is in contact with the liquid confinementstructure 12 due to the elasticity of the material of the barrier 220.The barrier 220 could be attached to the projection system PS in anotherway, for example by clamping or using a fastener. In an embodiment thebarrier 220 is glued, adhered or attached to liquid confinementstructure 12 and is in contact with the projection system.

FIG. 9 illustrates a further embodiment of the present invention. FIG. 9is a schematic cross-sectional view through a projection system PS andliquid confinement structure 12. The liquid confinement structure 12 maybe any type of liquid confinement structure, for example such as thatillustrated in FIG. 6. The embodiment of FIG. 9 is the same as theembodiment of FIG. 6 except as described below.

In the FIG. 9 embodiment, the gas space 200 is at least partly filled bya cellular material 700 made from a solid. The cellular material 700 isdesirably an open cell material. The cellular material 700 acts as abarrier in the same way as the barrier 220 in the form of a bellows ofthe FIG. 6 embodiment. The cellular material 700 may or may not beattached to one or both of the projection system PS and the liquidconfinement structure 12, for example by adhering. The cellular materialseals the gap between the projection system PS and the barrier 12.

The cellular material 700 extends vertically between the liquidconfinement structure 12 and the projection system PS. Therebysubstantially no forces are transferred between the projection system PSand the liquid confinement structure 12 through the cellular material700. Radially inward of the cellular material 700, there may be a gasspace 200 before the meniscus 210 of liquid or the meniscus 210 maytouch the cellular material 700.

As illustrated, the cellular material 700 is desirably present up to themeniscus 210 of liquid in the immersion space 11 which meniscus extendsbetween the liquid confinement structure 12 and the projection systemPS. The cellular material 700 has the effect of preventing evaporationof immersion liquid from, e.g., the projection system PS like theembodiment of FIG. 6. The cellular material prevents/substantiallyreduces evaporation in contrast to when no cellular material is present.A gas space radially inward of the cellular material 700 is passively(or actively) saturated resulting in a saturated gas space and reducedevaporation. Cells of the cellular material may comprise saturated gas,providing a localized saturated gas space in the cell. The cellularmaterial 700, as illustrated, extends substantially up to an edge 235 aof the projection system PS. The edge 235 a may either be the edge ofthe projection system PS as a whole or the edge of the final element ofthe projection system PS.

As in the barrier of the embodiment of FIG. 6, the cellular material 700is compliant substantially to prevent transmission of forces between theprojection system PS and the liquid confinement structure 12.

The presence of cellular material 700 is beneficial since it caneffectively reduce the free interaction of the immersion liquid with thegas at the other side of the cellular material 700. This reduces or eveneliminates the immersion liquid evaporation and its associated coolingeffect. The immersion liquid does not pass the cellular material 700.Thereby a lower thermal load is applied to the projection system. Thecellular material may allow passage of gas.

Immersion liquid may seep into the cells of the cellular material 700.This can be beneficial in one of two ways. First, the gas environment inthe cellular material may become saturated with vapor of the immersionliquid thereby reducing evaporational heat loads in the same way as thegas space 200 of the FIG. 6 embodiment. Alternatively or additionallythe immersion liquid may thereby be held in contact with the projectionsystem PS in the cells. This may have a same advantage as the embodimentof FIG. 10 described below and/or may have the additional advantage thatthe immersion liquid is confined within the cells so that substantiallyno splashing can occur.

Therefore, as can be seen, the cellular material 700 can be seen as aninsulator between the projection system PS and the liquid confinementstructure 12 in the same way as the saturated gas of the embodiments inFIGS. 6-8. The cellular material hinders or prevents gas and/or liquidfrom passing it in a radially outward direction and thereby functions asa seal. The seal transfers substantially no force between the projectionsystem PS and the liquid confinement system 12. In an embodiment thecellular material is a foam such as a sponge.

FIG. 10 shows a further embodiment. The embodiment of FIG. 10 is thesame as the embodiment of FIG. 9 except as described below. Embodimentsas shown in FIGS. 10-17 do not have any contact between the projectionsystem PS and the liquid confinement structure 12. That is, theprojection system PS and liquid confinement structure 12 and anystructure between the projection system PS and the liquid confinementstructure 12 and attached the projection system PS or liquid confinementstructure 12 are spaced apart. In all embodiments at least one of theprojection system PS and liquid confinement structure 12 is mechanicallydecoupled from the structure between the liquid confinement structure 12and the projection system PS. There is no interconnecting structurebetween the projection system PS and the liquid confinement structure12.

In the embodiment of FIG. 10 the meniscus 210 of immersion liquid isforced in a radially outward direction (all radial directions mentionedherein refer as an origin to the optical axis of the projection systemPS). Thereby, the meniscus 210 is positioned substantially at a radiallyouter edge 235 a of the projection system PS or at least a radiallyouter edge 235 a of the final element of the projection system PS. Inthis way no evaporation of immersion liquid from the surface, e.g.downwardly facing surface, of the final element of the projection systemPS is possible. By maintaining immersion liquid in contact with thatsurface of the final element of the projection system evaporation fromthat surface of immersion liquid is effectively prevented. Therefore, itcan be seen that the immersion liquid itself is insulating theprojection system PS from the liquid confinement structure 12,particularly because of the relatively high heat capacity of theimmersion liquid and its low coefficient of heat conduction.

In order to force the immersion liquid in a radially outward directionuse of capillary force and/or use of one or more liquidphilic surfacesmay be made. For example, the projection system PS and liquidconfinement structure 12 may be located close together and may have abottom surface and a top surface respectively shaped to cooperate suchthat a capillary gap 820 between the two components is formed. This hasthe effect of driving the liquid radially outwardly under capillaryaction. Alternatively or additionally the upwardly facing surface 800 ofthe liquid confinement structure 12 and/or the downwardly facing surface810 of the projection system PS may be made of a material or have acoating with which the immersion liquid has a receding contact angle ofless than 90°, desirably less than 80, 70, 60, 50, 40, 30, 20 or 10°(i.e. is liquidphilic). Such a measure also has the effect of forcingimmersion liquid in a radially outward direction compared to where itwould be if those surfaces did not have that property with regard to theimmersion liquid.

As is illustrated in FIG. 10, only the horizontal surfaces of the liquidconfinement structure 12 and the projection system PS are liquidphilicto the immersion liquid. However, other arrangements are possible. Forexample, only part of the horizontal surface may be liquidphilic to theimmersion liquid. Alternatively or additionally non horizontaldownwardly facing surfaces of the projection system PS and/or nonhorizontal upwardly facing surfaces of the liquid confinement structure12 radially inwardly of the horizontal surfaces illustrated could alsobe made to be liquidphilic to the immersion liquid. Desirably at leastthe part of the surface up to the edge 235 a of the projection system PSor final element of the projection system PS is made to be liquidphilicto the immersion liquid.

A further embodiment is illustrated in FIG. 11. The embodiment of FIG.11 is the same as the embodiment of FIG. 6 except as, described below.

In the embodiment of FIG. 11 no barrier is provided. However, in anembodiment a barrier may be provided.

In the embodiment of FIG. 11 a liquid supply device 252 is provided. Theliquid supply device 252 supplies liquid via an opening 253 to the gasspace 200. The liquid is desirably provided as a spray 254. In that casethe opening 253 may be a spray nozzle. Desirably the liquid is the sameas the immersion liquid.

The liquid may be provided in a radially inward direction, in a radiallyoutward direction, or both radially inward and radially outwarddirections, as illustrated. The liquid is desirably providedcontinuously. The liquid refreshment rate is higher than the possibleevaporation rate of liquid from the meniscus 210. This results in ahigher saturation in the gas space 200 than allows for evaporation ofliquid from the meniscus 210 or of droplets 205 on the projection systemPS.

In an embodiment the spray 254 is provided such that liquid contacts theprojection system PS, particularly the final element of the projectionsystem PS, desirably up to the edge 235. In this way evaporation fromthe final element of the projection system PS is reduced and thereby atemperature fluctuation can be reduced or avoided. Therefore, as withthe provision of saturated gas, the spray can be seen as an insulator ofthe projection system PS.

In other words, the liquid supply device 252 forces liquid (e.g., in aradially outward direction) in contact with the surface, e.g.,downwardly facing surface, of the final element of the projection systemPS. The liquid supply device 252 also maintains liquid in contact withthe surface of the final element of the projection system PS at aposition radially outward of the meniscus 210 extending between theprojection system PS and the liquid confinement structure 12.

Although the liquid supply device 252 and opening 253 are illustrated asbeing formed in the liquid confinement structure 12, this is notnecessarily the case. In an embodiment the liquid supply device 252 andopening 253 may be formed in a member separate from the liquidconfinement structure 12 and the projection system PS. In an embodiment,the liquid supply device 252 and/or the opening 253 is provided in theprojection system PS.

FIG. 12 illustrates a further embodiment which is the same as theembodiment of FIG. 6 except as described below.

In the embodiment of FIG. 12, a wetting medium 600, which may be made offibrous material, is provided on the projection system PS. The wettingmedium 600 may be a sheet and may be in the form of mesh or sheet mesh.The wetting medium 600 is attached to the final element of theprojection system PS. For example the wetting medium may be attached toa surface by adherence. The wetting medium 600 is positioned in an areawhere splashing of immersion liquid onto the final element of theprojection system is likely.

The wetting medium 600 desirably extends to a position where its end isnormally covered by immersion liquid in the immersion space, Capillaryaction draws liquid up into the mesh 600 from the immersion space.Thereby the wetting medium 600 is substantially always wet withimmersion liquid during projecting of the patterned beam.

The wetting medium 600 draws immersion liquid up and, for example, in aradially outward direction (e.g. forces the liquid up) and in contactwith a surface, e.g. a downwardly facing surface, of the final elementof the projection system PS. The wetting medium 600 also maintainsliquid in contact with the surface of the final element of theprojection system PS radially outward of the meniscus 210 extendingbetween the projection system and the liquid confinement structure 12.

Additionally or alternatively, any splashes of liquid which fall on thewetting medium 600 are quickly spread out. So any heat load applied byevaporation of that liquid is not applied to a small localized area butapplied over a larger area covered by the wetting medium 600.

The wetting medium 600 may be any porous media having adequateporosity/permeability (e.g. enough capillary force) to draw the liquidupwards. In an embodiment the wetting medium 600 is a mesh.

In an embodiment the wetting medium 600 is substantially always wet andliquid evaporates from it. This results in saturated immersion liquidvapor being adjacent to the meniscus 210. Thereby in this embodiment itis accepted that a thermal load is applied to the projection system PSbut that thermal load is maintained substantially constant by arrangingfor the wetting medium 600 to substantially constantly be wet. Becausethe thermal load is substantially constant, this can be compensated forby other measures in known ways.

A further embodiment is illustrated in FIG. 13. The embodiment of FIG.13 is similar to the embodiment of FIG. 10 in that it uses the principlethat if immersion liquid is present on a surface in bulk, then it cannotimpart a significant heat load on the projection system PS due toevaporation. By bulk liquid it is meant liquid which is not droplets andwhich is desirably in contact with the liquid in the space 11.Therefore, in the embodiment of FIG. 13 a device is provided to maintainimmersion liquid in contact with the surface, e.g., the downwardlyfacing surface, of the final element of the projection system radiallyoutwardly of the meniscus 210 extending between the projection system PSand the liquid confinement structure 12. In the embodiment illustratedin FIG. 13 this is achieved by providing a projection 900 which extendsfrom the projection system PS. The projection 900 extends radiallyinwardly toward the optical axis. The projection 900 extends downwardlytowards the liquid confinement structure 12. The projection 900 may haveany shape, in cross-section. In plan, the projection 900 surrounds theoptical axis of the projection system PS.

The meniscus 210, which extends between the projection system PS and theliquid confinement structure 12, extends between a free end of theprojection 900 and the liquid confinement structure 12. Radiallyoutwardly of the position of the meniscus 210, immersion liquid ismaintained in contact with the surface, e.g. a downwardly facingsurface, of the projection system up to the position 235 b where theprojection 900 is attached to the surface of the projection system PS.The position 235 b may be at the radially outer most edge of the finalelement of the projection system PS or may be at the radially outwardmost position of the projection system PS as a whole, for example.However, the position 235 b may be at any other location.

The projection 900 may be, for example annular, with a lower edge havinga smaller radius than an upper edge.

The projection 900 does not contact the liquid confinement structure 12.This is advantageous as it therefore does not transfer forces betweenthe projection system PS and the liquid confinement structure 12.Furthermore, if the position of the meniscus 210 varies slightly, thisvariation in position of attachment is on the liquid confinementstructure 12 which is not as sensitive as the projection system PS tovariations in temperature (for example due to evaporation).

The meniscus 210 may be pinned to the free end of the projection 900.For example, this may be achieved by providing a change in contact angleof the immersion liquid to the surface of the projection 900 at the freeend. Alternatively or additionally, the free end may be made sharpthereby to pin an end of the meniscus 210 to the free end of theprojection 900. The free end of the projection 900 may have a point. Theprojection 900 may be flexible to allow certain movement between theliquid confinement structure 12 and the projection system.

In an embodiment, the projection is attached to the liquid confinementstructure 900 and a meniscus 210 interconnects the projection to thesurface of the projection system. The arrangement is otherwise asdescribed for the embodiment shown in FIG. 13.

FIG. 14 shows a further embodiment of the present invention. Theembodiment of FIG. 14 is the same as the embodiment of FIG. 6 except asdescribed below. The embodiment of FIG. 14 has similarities with theembodiments of FIGS. 10, 12 and 13 in that it works on the principlethat if the bulk of the immersion liquid is in contact with a surface ofthe projection system PS, a low heat load will be applied to thatsurface due to evaporation of the liquid.

In the embodiment of FIG. 14 a device 1000 is provided which forcesimmersion liquid in a radially outward direction while it is in contactwith the surface, e.g. a downwardly facing surface, of the final elementof the projection system PS. In the embodiment of FIG. 14 this device isa member 1000. A capillary passage is formed between the member 1000 andthe surface of the projection system PS. Liquid from the space 11 isdrawn up between the member 1000 and the surface thereby to be incontact with the surface and reduce heat loads applied to the projectionsystem PS in the same way as the embodiments of FIGS. 12 and 13.

Desirably the surface of the member 1000 facing the surface of the finalelement of the projection system PS and/or the surface of the finalelement of the projection system PS are made to be lyophilic to theimmersion liquid, as in the embodiment of FIG. 10.

As can be seen, as with the embodiment of FIG. 13, the meniscus 210extends between the liquid confinement structure 12 and an end of themember 1000. The end of the member 1000 to which the meniscus 210 isattached is the radially inner most free end. That radially inner mostfree end may be treated as in the same way as the free end of theprojection 900 of the embodiment of FIG. 13 in order to pin an end ofthe meniscus 210 to it. In an embodiment, the meniscus 210 may extendbetween the liquid confinement structure 12 and the outwardly facingsurface of the member 1000.

The member 1000 may be attached to the projection system or to a finalelement of the projection system or to a mount or casing of theprojection system PS. It is desirable that the member 1000 is connectedto a component other than the projection system, such as its mounting orhousing. This is desirable as it would reduce the transfer of forcesand/or a thermal load to the projection system. The forces may bedisturbance forces from outside the member 1000 or outside theprojection system. The forces may be caused by the immersion liquid, thesubstrate table WT, the liquid confinement structure 12 or movement ofthe substrate W. In an alternative embodiment, the member 1000 is fixedin place to the projection system PS by capillary force. Alternatively,the member 1000 may be attached to the liquid confinement structure 12,though this is less desired, or to any other structure.

The member 1000 may be attached in any way to the projection system PSor other structure. For example, a plurality of discrete attachmentmembers may be provided in the capillary channel between the member 1000and the projection system PS in order to attach it to the projectionsystem PS.

The member 1000 is generally plate like and is shaped so that itssurface which faces the projection system PS closely conforms in shapeto the surface of the projection system PS. Therefore, as can be seenfrom FIG. 14, the member 1000 ensures that immersion liquid ismaintained in contact with the surface of the final element of theprojection system PS radially outwardly of the meniscus 210 extendingbetween the projection system PS and the liquid confinement structure12.

The member 1000 may be made to a desired length so that a desired amountof the surface of the projection system PS is covered. In an embodiment,all of the surface, e.g. a downwardly facing surface, of the finalelement of the projection system PS is covered. That is, the member 1000extends substantially to the radially outer edge of the final element ofthe projection system PS, or further radially outwardly thereof. In analternative embodiment, the element 1000 may extend even further, forexample to the edge of the projection system PS as a whole.

The surface of the member 1000 facing away from the projection systemmay be made lyophobic. A lyophobic surface may be desirable as a dropletof immersion liquid is less likely to form on such a surface. A heatload applied by the droplet may be avoided.

A further embodiment is illustrated in FIG. 15. The embodiment of FIG.15 is the same as the embodiment of FIG. 6 except as described below.

To prevent fluctuations in pressure of immersion liquid in the immersionspace due to scan movements affecting the fluid level at the top of theliquid confinement structure 12, the immersion space is divided into anupper volume 11 a and a lower volume 11 b. This division is made by atransparent plate 1100. Therefore, the upper volume and lower volume 11a, 11 b are not in fluid communication and the thermal stability andposition of the meniscus 210 in the upper volume 11 a can be controlledmore accurately. Thereby changes in position of the meniscus 210 can bereduced and the chance of splashing occurring and thereby dropletsforming on the projection system PS is also reduced. The transmissiveplate 1100 desirably has high transmissivity at the wavelength of theprojection system PS and, in an embodiment, a refractive index as closeas possible to that of the liquid in either or both the upper and lowervolumes 11 a, 11 b. The transmissive plate 1100 is desirably flat andplane parallel to enable desired imaging requirements to be met. Anydeviations from flat (e.g. due to gravity) can be compensated for by theprojection system PS as described in U.S. Patent Application PublicationNo. 2005/0280789. Individual openings for provision and extraction ofliquid to the upper and lower volumes 11 a, 11 b are provided in theliquid confinement structure 12.

The liquid in the upper volume 11 a is different to the liquid in thelower volume 11 b. For example, the liquid in the upper volume 11 a mayhave a different temperature to liquid in the lower volume 11 b.Alternatively or additionally the composition or concentration of theliquid in the upper volume 11 a may be different to the composition orconcentration in the lower volume 11 b.

FIG. 16 illustrates a further embodiment. The embodiment of FIG. 16 isthe same as the embodiment of FIG. 15 except as described below.

In the FIG. 16 embodiment the immersion space 11 is not separated intoupper and lower volumes. However, a member 1200 is provided to define avolume 1210 between an edge of the final element of the projectionsystem PS and the member 1200. This volume 1210 is filled with a fluidto thermally condition the final element of the projection system PS.

The volume 1210 surrounds the optical axis of the projection system PSand the projection beam B does not pass through it. That is, the volume1210 does not extend to underneath the lower surface of the finalelement of the projection system PS through which the projection beamexits the projection system PS. The member 1200 seals the bottom of thevolume 1210 from being in fluid communication with the immersion space11 at the bottom of the volume 1210.

The meniscus 210 extends between the liquid confinement structure 12 andthe member 1200. Any changes in position of the meniscus 210 or dropletsforming on the member do not substantially affect the temperatureprofile of the final element of the projection system PS because thefluid in the volume 1210 is effective to insulate the projection systemPS from thermal fluctuations. Thus, the fluid in the volume 1210 can beseen as an optical element insulator which lies outside of an opticalpath of the apparatus.

A fluid supply device 1250 supplies fluid to the volume. The fluidsupply device 1250 may include a fluid conditioning device to conditionthe temperature of the fluid entering the volume 1210. The fluid may beany fluid provided it is chemically compatible with materials of thefinal element of the projection system PS and the member 1200.

In an alternative embodiment, the volume 1210 may be comprised of aplurality of discrete channels. Fluid may be provided individually toeach of those discrete channels at a desired temperature. The desiredtemperature may be determined in a feedforward manner, for example. Inan embodiment, a sensor 1230 is associated with the or each of thechannels. A controller 1260 can then adjust the temperature of the fluidprovided to the channel(s) dependent upon the temperature measured bythe sensor 1230 associated with the channel. This may be controlled in afeedback loop.

A similar embodiment to that of the FIG. 16 embodiment is illustrated inFIG. 17. The FIG. 17 embodiment works on the same principle as the FIG.16 embodiment of insulating the optically active part of the projectionsystem. This is achieved by making the final element of the projectionsystem PS larger than it needs to be. The final element of the FIG. 17embodiment comprises an optically active part 1300 through which theprojection beam PB (illustrated by cross-hatching) passes and anoptically inactive part 1310 which lies outside of the optical path ofthe apparatus. The optically inactive part 1310 surrounds the opticalaxis and the final element of the projection system PS around an outeredge. The final element insulator does not extend to the bottom of theprojection system PS and thereby lies outside of an optical path of theapparatus. The optically inactive part 1310 acts as an insulator helpingto ensure that any temperature variation 2205 which occurs, for exampledue to an evaporating droplet 205, are substantially dampened out beforethey reach the optically active part 1300 of the final element of theprojection system PS. Thus, as in the embodiment of FIG. 16, theoptically active part 1300 of the projection system PS is insulated froma thermal variation. The optically inactive part 1310 is desirably atleast 3 mm thick.

Instead of making the final element of the projection system PS largerthan necessary, it is possible to apply a coating to the radially outeredge of the final element of the projection system PS outside of theoptical path of the apparatus.

Desirably the lithographic apparatus comprises a liquid confinementstructure which has a surface which surrounds the immersion space and atleast partly defines a boundary of the immersion space. Desirably theliquid confinement structure is substantially stationary relative to theprojection system. Desirably the liquid confinement structure confinesliquid to a localized area of the top surface of the substrate.

The embodiments of FIGS. 6 to 9 may be used in a mode similar to that ofFIG. 10. That is, the meniscus 210 of the immersion liquid from theimmersion space 11 may extend radially outward to the vicinity of or upto the barrier 220 or cellular material 700. The meniscus 210 may bepinned at the barrier 220 or cellular material 700. The barrier 220 orcellular material 700 may be radially outward or radially inward orcoincide with an edge of a surface of the projection system (such as afinal element of the projection system), which may be adversely affectedby unregulated temperature fluctuations as a consequence of interactionwith evaporating immersion liquid. In an embodiment, the immersionliquid is in contact with an entire surface of the projection system PS,for example the final element, such as the lower surface of the finalelement. The immersion liquid may help maintain the temperature of thesurface of the projection system which interacts and/or contactsimmersion liquid. Desirably the surface temperature of the projectionsystem in the immersion system may thereby be regulated. A fluctuationin the surface temperature of the projection system which may contactthe immersion system may be reduced, if not prevented.

A further embodiment is illustrated in FIG. 18 and is the same as theembodiment of FIG. 6 except as described below. The embodiment uses amember 130 which is placed adjacent an optically active part of a finalelement of the projection system PS. In use, the member is between theimmersion liquid and the optically active part.

The member 130 is configured to spread a heat load applied to alocalized area of the member by immersion liquid on it onto an area ofthe optically active part greater than the localized area. The heat loadmay be applied, e.g., through droplets of the immersion liquid orthrough immersion liquid from the immersion space 11.

The spreading of the heat load to an area greater than the localizedarea is achieved by thermal conduction. That is, the member 130 iscomprised of a material with a high thermal conductivity (for instance,a material with a higher coefficient of thermal conductivity than thematerial of the optically active part of the projection system PS). Inthis way any temperature variation on the member is quickly evened outby thermal conduction. In this way the heat load applied on one side ofthe member is spread out before any significant effect is felt on theother side of the member (which is close to the optically active part ofthe projection system PS).

The member 130 is positioned adjacent the optically active part of thefinal element of the projection system PS. The member 130 lies outsideof the optical path of the apparatus. The member 130 surrounds theoptical axis of the apparatus and the final element of the projectionsystem PS around an outer edge. As illustrated, the member 130 does notextend to the bottom of the projection system PS and thereby liesoutside of the optical path of the apparatus. The member 130 extendsinto the immersion space 11 so that a meniscus 210 of liquid in theimmersion space 11 extends between the member 130 and the liquidconfinement structure 12.

The member 130 may be spaced from the final element of the projectionsystem PS. In this way a gap 131 exists between the member 130 and theprojection system PS. This gap 131 may be filled with gas or aninsulator or may be maintained under a vacuum. The presence of the gap131 helps to ensure that any temperature variation which does occur inthe member 130 is not substantially transmitted into the final elementof the projection system PS. A seal 132 may be formed between an end ofthe member 130 and the final end of the projection system PS at thebottom of the projection system PS.

The member 130 may be attached to the final end of the projection systemPS by adherence, for example away from the final end of the projectionsystem PS. For example, the member 130 could be glued to the final endof the projection system PS. Other means of fixing the member 130 to thefinal end of the projection system PS are possible. In an embodiment,the member 130 is not spaced from the final element of the projectionsystem PS.

In an embodiment, the member 130 is dynamically isolated from the finalend of the projection system PS. There may be a dynamic isolator betweenthe member 130 and the final end of the projection system PS. The member130 may help to prevent pressure fluctuations of the liquid in theimmersion space 11 which would otherwise cause undesired vibrations ofthe final end of the projection system PS. Undesired vibrations of thefinal end of the projection system PS are undesired because they maydeteriorate the image projected on the target portion of the substrate.

A droplet 205 which lands on the member 130 can evaporate and therebygenerate a head load on the member 130. Because the member 130 is of amaterial with a high coefficient of thermal conductivity, the heat loadwill quickly be dissipated throughout the member 130. This heatdissipation can be aided by having the end of the member 130 immersed inimmersion liquid in the immersion space 11. This helps ensure thethermal stability of the member 130. That is, the member 130 isthermally conditioned by the immersion liquid.

In an embodiment, the member 130 is in the form of a coating and thereis no gap 131.

In an embodiment, the projection system has a lower surface; and theimmersion space comprises, in use, a liquid with a meniscus between apart of the lower surface and a facing surface of the liquid confinementstructure facing the part of the lower surface; wherein a pinningsurface comprises a plurality of meniscus pinning features, the pinningsurface being the part of the lower surface facing the surface of theliquid confinement structure, or the surface of the liquid confinementstructure facing the lower surface, or both.

By providing the part of the lower surface facing the surface of theliquid confinement structure or the surface of the liquid confinementstructure facing the part of the lower surface, or both, with aplurality of meniscus pinning features the movement of the meniscus 210due to sloshing is reduced. A plurality of meniscus pinning features maybe useful, for example, as there may not be a single meniscus heightposition around the periphery of the lower surface. There may bedifferences between the same types of immersion lithographic apparatusresulting in a different height position of the meniscus within theseapparatus. Within one apparatus, a changed operating condition of theapparatus may alter the height position of the meniscus. For example inhaving the liquid confinement structure displaced at different distancesaway from the lower surface, such as when lowering or raising the liquidconfinement structure, or operating at different relative speeds(scanning speeds) the position of the meniscus will change.

Desirably the plurality of meniscus pinning features comprises more thanone type of pinning feature which repeats in series over the pinningsurface. Desirably one of the types of feature is a first surface andanother of the types of feature is a second surface with differentsurface contact angle than that of the first surface. Desirably thefirst surface is lyophilic and the second surface is lyophobic. In anembodiment, one of the types of feature is a protrusion and another ofthe types of feature is a recess. Desirably at least some of theplurality of protrusions define a plurality of steps, and/or at leastsome of the plurality of protrusions comprises a plurality of groovesand/or the plurality of protrusions are substantially randomly locatedalong a direction away from an optical axis of the projection system.Desirably the surface of each of the protrusions has a displacement ofbetween 1 and 1000 μm from a mean contour, wherein the mean contour isthe average displacement of the multiple pinning features of the pinningsurface relative to a reference surface. Desirably the series offeatures repeats in a direction away from an optical axis of theprojection system. Desirably a pitch is defined between adjacentfeatures and the pitch is smaller than 5 mm. In an embodiment at leastone of the pinning features comprises a fiber. Desirably the pluralityof meniscus pinning features are present substantially around thecomplete periphery of the part of the lower surface facing the surfaceof the liquid confinement structure, or the surface of the liquidconfinement structure facing the part of the lower surface, or both. Inan embodiment, the liquid confinement structure or the projection systemcomprise a removable component comprising the pinning surface. Desirablythe removable component is an adhesive sheet. Desirably the removablecomponent comprises metal.

It may be possible to combine certain embodiments. For example, any ofembodiments of FIGS. 6-11 and the plurality of pinning featuresembodiment could be combined with any of the embodiments of FIGS. 14-18.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may refer to a substrate thatalready contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

Controllers described above may have any suitable configuration forreceiving, processing, and sending signals. For example, each controllermay include one or more processors for executing the computer programsthat include machine-readable instructions for the methods describedabove. The controllers may include data storage medium for storing suchcomputer programs, and/or hardware to receive such medium.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above, whether the immersion liquid is provided in the form ofa bath, only on a localized surface area of the substrate, or isunconfined on the substrate and/or substrate table. In an unconfinedarrangement, the immersion liquid may flow over the surface of thesubstrate and/or substrate table so that substantially the entireuncovered surface of the substrate table and/or substrate is wetted. Insuch an unconfined immersion system, the liquid supply system may notconfine the immersion liquid or it may provide a proportion of immersionliquid confinement, but not substantially complete confinement of theimmersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more liquid inlets, one ormore gas inlets, one or more gas outlets, and/or one or more liquidoutlets that provide liquid to the space. In an embodiment, a surface ofthe space may be a portion of the substrate and/or substrate table, or asurface of the space may completely cover a surface of the substrateand/or substrate table, or the space may envelop the substrate and/orsubstrate table. The liquid supply system may optionally further includeone or more elements to control the position, quantity, quality, shape,flow rate or any other features of the liquid.

Moreover, although this invention has been disclosed in the context ofcertain embodiments and examples, it will be understood by those skilledin the art that the present invention extends beyond the specificallydisclosed embodiments to other alternative embodiments and/or uses ofthe invention and obvious modifications and equivalents thereof. Inaddition, while a number of variations of the invention have been shownand described in detail, other modifications, which are within the scopeof this invention, will be readily apparent to those of skill in the artbased upon this disclosure. For example, it is contemplated that variouscombination or sub-combinations of the specific features and aspects ofthe embodiments may be made and still fall within the scope of theinvention. Accordingly, it should be understood that various featuresand aspects of the disclosed embodiments can be combined with orsubstituted for one another in order to form varying modes of thedisclosed invention. Thus, it is intended that the scope of the presentinvention herein disclosed should not be limited by the particulardisclosed embodiments described above, but should be determined only bya fair reading of the claims that follow.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

In an embodiment, there is provided a lithographic apparatus, comprisinga projection system and a liquid confinement structure configured atleast partly to confine immersion liquid to an immersion space definedby the projection system, the liquid confinement structure and asubstrate and/or substrate table. The lithographic apparatus furthercomprises a barrier extending from the projection system to the liquidconfinement structure and around the optical axis of the apparatus tosubstantially seal a gap between the projection system and the liquidconfinement structure. The barrier is compliant substantially to preventtransmission of forces between the projection system and the liquidconfinement structure.

The barrier may be attached to only one of the projection system and theliquid confinement structure. The barrier may also be in contact withthe other of the projection system and liquid confinement structure. Thebarrier may be attached to both the projection system and the liquidconfinement structure. Alternatively, the barrier may not be attached toeither the projection system or the liquid confinement structure.

The barrier may be held in contact with the projection system and/or theliquid confinement structure by the elasticity of the material of thebarrier. For example, the barrier is a bellows.

The barrier may extend from a mounting or shielding structure of theprojection system to the liquid confinement structure. The barrier maybe made of a cellular material, for example an open cell material.

In an embodiment, a lithographic apparatus may comprise a gas spacewhich is defined between the projection system, the liquid confinementstructure, the barrier and, in use, the immersion liquid in theimmersion space. The gas space may be configured to contain gassubstantially saturated with vapor of the immersion liquid. Thelithographic apparatus may further comprise a gas source configured toprovide gas substantially saturated with vapor of the immersion liquidto the gas space.

During use of the lithographic apparatus, a bulk of immersion liquid inthe immersion space may extend substantially to the barrier. In anembodiment, the stiffness of the barrier is less than 1 N/mm. In anembodiment, the liquid confinement structure may allow, in use, liquidto flow onto a top surface of a substrate radially outwardly of theimmersion space. The liquid confinement structure may comprise featuresto form a contactless seal with the substrate to confine liquid to theimmersion space.

In an embodiment, a lithographic apparatus may comprise a projectionsystem and a liquid confinement structure to at least partly confineimmersion liquid to an immersion space defined by the projection system,the liquid confinement structure and a substrate and/or substrate table.The lithographic apparatus may further comprise a device to forceimmersion liquid in a radially outward direction and in contact with asurface of the final element of the projection system and/or to maintainliquid in contact with the surface of the final element of theprojection system radially outward of a meniscus extending, in use,between the projection system and the liquid confinement structure.

The projection system, the liquid confinement structure, and anystructure between the projection system and liquid confinement structureand attached to the projection system or liquid confinement structure,may be spaced apart. The projection system and/or the liquid confinementstructure may be mechanically decoupled from the device. The device maycomprise an opening for the provision therethrough of immersion liquidonto the surface. The opening may be in the liquid confinementstructure. The opening may be a spray nozzle. The device may beconfigured to force immersion liquid in a radial outward direction ormaintain immersion liquid in contact with the surface of the finalelement of the projection system by capillary force. The device maycomprise a wetting medium attached to the final element of theprojection system. The device may comprise a member positioned between apart of the final element of the projection system and the liquidconfinement structure, wherein a capillary passage to force immersionliquid in a radially outward direction is formed between the member andthe final element of the projection system. The member may be a platemember shaped closely to conform with the shape of the surface of thefinal element.

The device may be configured to maintain immersion liquid in contactwith the surface of the final element of the projection system radiallyoutward of a meniscus extending, in use, between the projection systemand the liquid confinement structure. The device may comprise aprojection extending from the projection system, desirably radiallyinwardly, towards the liquid confinement structure. The projection mayextend around the optical axis of the apparatus. The projection may notcontact the liquid confinement structure and the meniscus, in use,extending between the projection system and the liquid confinementstructure extends between the free end of the projection and the liquidconfinement structure.

The device may be configured to maintain immersion liquid in contactwith the surface of the final element of the projection system.

The device may be configured to maintain a liquid other than immersionliquid in contact with the surface of the final element of theprojection system.

A volume may be defined between a member of the device and an edge ofthe final element of the projection system radially outwardly of abottom surface of the final element of the projection system. The membermay seal the volume from being in fluid communication with immersionliquid at a bottom end of the volume. The volume may be filled with afluid. The lithographic apparatus may further comprise a fluidconditioning unit configured to condition the temperature of fluid inthe volume. In use, a meniscus of immersion liquid may extend betweenthe liquid confinement structure and the member. The volume may comprisea plurality of discrete channels. The lithographic apparatus may furthercomprise a plurality of sensors and a controller. Each sensor may beassociated with a channel and configured to detect a temperature in thevicinity of the associated channel. The controller may be configured toadjust the temperature of fluid in each channel dependent upon themeasured temperature by the associated sensor.

In an embodiment, a lithographic apparatus may comprise a surface withwhich the immersion liquid has a receding contact angle of less than90°, desirably less than 80, 70, 60, 50, 40, 30, 20 or 10°. The surfacemay be a surface of the projection system and/or a surface of thebarrier or device and may include at least a surface of a final elementof the projection system.

In an embodiment, the device may be arranged to force the immersionliquid by capillary action, desirably wherein capillary action occursbetween an upwardly facing surface of the liquid confinement structureand the downwardly facing surface of the final element of the projectionsystem.

In an embodiment, a lithographic apparatus is provided with an opticalelement insulator located between an optically active part of aprojection system and a liquid confinement structure. The opticalelement insulator may lie outside of an optical path of the apparatus.The optical element insulator may be material of the final element ofthe projection system which is not optically active and may be at least3 mm thick. The optical element insulator may be a coating on a surfaceof a final element of the projection system and may be adhered to thefinal optical element of the projection system. In use, a meniscus ofliquid may extend between the optical element insulator and the liquidconfinement structure. The optical element insulator may comprise aliquid. The liquid may be separate from liquid through which a beam ofradiation passes during imaging of a substrate.

In an embodiment, a lithographic apparatus may comprise a projectionsystem and a liquid confinement structure configured at least partly toconfine immersion liquid to an immersion space defined by projectionsystem, the liquid confinement structure and a substrate and/orsubstrate table. The liquid confinement structure may be partitionedinto an upper volume and a lower volume which are separated by atransmissive plate. The liquids in the upper volume and the lower volumemay be different. The upper liquid and lower liquid may be different inrespect of at least property selected from the following properties:temperature, composition, or concentration.

1. A lithographic apparatus, comprising: a projection system; a liquidconfinement structure configured at least partly to confine immersionliquid to an immersion space defined by the projection system, theliquid confinement structure and a substrate and/or substrate table; anda barrier extending from the projection system to the liquid confinementstructure and around the optical axis of the apparatus to substantiallyseal a gap between the projection system and the liquid confinementstructure, wherein the barrier is compliant substantially to preventtransmission of forces between the projection system and the liquidconfinement structure.
 2. The lithographic apparatus of claim 1, whereinthe barrier is attached to only one of the projection system and theliquid confinement structure.
 3. The lithographic apparatus of claim 2,wherein the barrier is in contact with the other of the projectionsystem and liquid confinement structure.
 4. The lithographic apparatusof claim 1, wherein the barrier is attached to both the projectionsystem and the liquid confinement structure.
 5. The lithographicapparatus of claim 1, wherein the barrier is not attached to either theprojection system or the liquid confinement structure.
 6. Thelithographic apparatus of claim 1, wherein the barrier is held incontact with the projection system and/or the liquid confinementstructure by the elasticity of the material of the barrier.
 7. Thelithographic apparatus of claim 1, wherein the barrier is a bellows. 8.The lithographic apparatus of claim 1, wherein the barrier extends froma mounting or shielding structure of the projection system to the liquidconfinement structure.
 9. The lithographic apparatus of claim 1, whereinthe barrier is made of a cellular material.
 10. The lithographicapparatus of claim 9, wherein the cellular material is an open cellmaterial.
 11. The lithographic apparatus of claim 1, wherein a gas spaceis defined between the projection system, the liquid confinementstructure, barrier and, in use, the immersion liquid in the immersionspace.
 12. The lithographic apparatus of claim 11, wherein the gas spaceis configured to contain gas substantially saturated with vapor of theimmersion liquid.
 13. The lithographic apparatus of claim 11, furthercomprising a gas source configured to provide gas substantiallysaturated with vapor of the immersion liquid to the gas space.
 14. Thelithographic apparatus of claim 1, wherein, in use, a bulk of immersionliquid in the immersion space extends substantially to the barrier. 15.The lithographic apparatus of claim 1, wherein the stiffness of thebarrier is less than 1 N/mm.
 16. The lithographic apparatus of claim 1,wherein the liquid confinement structure allows, in use, liquid to flowonto a top surface of a substrate radially outwardly of the immersionspace.
 17. The lithographic apparatus of claim 1, wherein the liquidconfinement structure comprises features to form a contactless seal withthe substrate to confine liquid to the immersion space.
 18. Alithographic apparatus, comprising: a projection system; a liquidconfinement structure to at least partly confine immersion liquid to animmersion space defined by the projection system, the liquid confinementstructure and a substrate and/or substrate table; and a device to forceimmersion liquid in a radially outward direction and in contact with asurface of the final element of the projection system and/or to maintainliquid in contact with the surface of the final element of theprojection system radially outward of a meniscus extending, in use,between the projection system and the liquid confinement structure. 19.A lithographic apparatus wherein an optical element insulator is locatedbetween an optically active part of a projection system and a liquidconfinement structure and the optical element insulator lies outside ofan optical path of the apparatus.
 20. A lithographic apparatus,comprising: a projection system; and a liquid confinement structureconfigured at least partly to confine immersion liquid to an immersionspace defined by projection system, the liquid confinement structure anda substrate and/or substrate table, wherein the liquid confinementstructure is partitioned into an upper volume and a lower volume whichare separated by a transmissive plate, wherein the liquids in the uppervolume and the lower volume are different.